Phantom carrier circuits



April 27 1.926.

H. A. AFFEL PHANTOM CARRIER CIRCUITS Filed August 11. 1925 INVENTOR44760 ATTORNEY Patented Apr. 27, 1926.

- UNITED. STATES PATENT OFFICE.

HERMAN A. AFFEL, or vrArLEwoon, Nnw'JERsR-Y, 'ASSIGNOR'TO AMRRIcAN-TELE- PHONE AND 'TELEGBAJEI COMPANY, A ooRPo-RA rIoN or NEW YORK.

PHANTOM cARRIER CIRCUITS.

Application filed August 11, 1925. Serial No. 49,608.

To all whom itmag concem:

Be it. known that I, 'H RMAN A. AFFEL, a citizen of the United States,residing at Maplewood, in the county of Essex and State of New. Jersey,have invented certain Improvements in Phantom Carrier Circuits, of whichthe followingis a specification.

This invention relates to transmission circuits and more particularly toarrangements for employing carrier transmission upon phantom,conductiv'e systems. a

It has heretofore been the practice in ordinary telephone transmissionto "Fphantom the telephone circuits so that each pair of conductorsnotonly acts as a seriesconvductive system or a side circuit, but alsoacts as one side ofa phantom circuit, 'the two conductors in parallelconstituting one conductor of the phantom path while the two conductorsof a similar side circuit operate in parallel as thereturn path for thephantom circuit. It ,has not, however, been the practice to utilize thephantom circuits thus formed for carrierqtransmission because-therequirements with respect tonnbalance and crosstalk-at-carrierfrequencies have. been too great. .Thecarrier frequency unbalance andcrosstalk ofthe phantom are gradually being reduced, however, and thereis now presentedthe problem "of associating filters with each other soas to p'rop cr'ly separate the side voice circuits f and side carriercircuits from each otherand at the same time separate the phantom voicecircuit and phantom carrier circuit from, each other and from the sidecircuit channels. I

It is one of the objects of the present invention to provide a suitablearrangement of filters for efiecting'the necessary separation betweenthe various typesof circuits without introducing undesirable.transmission losses and without producing any undesirable efliect's uponthe filters f due to the presence in. filters.

These objectsas wellasother objectsoi the invention may beattainedlby.meansof the arrangements set forth in the (followingdescription and illustrated in the acCQInpanying drawing, the figure Vof which: shows a ircuit diagram e bdt yi igtheinVntiQn1n;ltspreferred-form. A

,to the voice side circuit channel-VL the same network ofotlierReferring to the drawing, HFL and I-IFLrepresent two telephonelines,each comprising a pair. of conductors which may be phantomed in a wellknown manner so that each pair of conductors acting in parallel operatesas one side of a phantom circuit. The phantom connections are established by means of transformers 10 and 10, from the middle points ofwhose windings taps 11 and 11 are led to form the phantom tern-finals.of the system; Con'ipositesets and OX are included inthei line HFL andHFL by means of which each olthc I fours conductors may be employed forMorse telegraph transmission. 'Thecomposite sets are. merelyshownschematicallyin the drawmg, these sets being or" a type well knownin the art so that detailed illustration is unnecessary. A v

In orclei'tliat thelineHFLrmay be em- .Jlo'yed foi ca 'riertransmission, a branch L is provided which leads to carrier equipment ofany type Well known in the art. and, in thisbranch'a high pass filter.HF is included. This higlrpass filter is ofthe broad band type whichfreely transmits aband of frequencie within certain limits, whilesharply attenuating andsuppressing the frequencieslying without thelimits of the band. The filter is so designedasto pass the" variouscarrier frequencies employed in the system together with theirassociated'side bands, but it'will not permit ordinary voice currentstransmittedover the line HFL to pass into the ,circuitCL Theordinaryvoice currents transmitted over the conductor HFL must be separated fromthe carrierfrequencies and transmitted through the transformer 10 Inorder to accomplish this result, a low pass .filter LF is connectedinthe branch of the line circuitrHFL leading to the voice side circuit iVLThe filter LF is of the broad band type and freely transmits allfreouencies. lying Within the voice range while suppress ng allfrequencies above the voicerange- .llhe carr er pfrequenclesare therebying through the loss pass filter LF to the voice side circuit VL Thearrangement so far described is that ordinarily employed for superposinga plurality of carrier channels on an ordinary voice channel. It ispossible to phantom a pair of circuits of this type for ordinary voicetransmission by means of the phantom coils l0 and 10 with their phantomconductors 11 and 11. This follows at once from the fact that theunbalance between the phantom circuit and the side circuits at voicefrequencies is no greater with the arrangement above described than inthe case of circuits which are not arranged for mul tiplex carriertransmission, and the voice currents transmitted over the phantom, in sofar as any unbalance occurs between the two conductors of the sidecircuit, are prevented from entering the carrier circuit, such as thecircuit GL by the high pass filter. The effect upon the phantom of thefilter LF -in the two conductors of the side circuit is to introduceimpedance due to the series coils of the filter but this impedance isnot serious at the ordinary voice frequencies. If, however, we attemptto transmit carrier frequencies over the phantom,

the inductance of the series elements of the filter L13 of LF, isrelatively much greater, so that not only must this problem be overcomebut the problem of selection between the carrier phantom and the voicephantom must also be overcome.

In accordance with the present invention, therefore, it is proposed totransmit the phantom carrier currents over the carrier branchesincluding the filters HF and HR. For this purpose,phantom coils'20 and20 are included in the circuits CL, and Chg as indicated, and phantomconductors 2i and 21 are led from the midpoints of .the phantom coils toform a carrier phantom terminal 011 With this arrangement, the phantomcarrier currents need only be transmitted through the impedance of 'thefilters HF, and H1 The shunt elements of these filters are inductancecoils bridged across equal potential points (with respect to thephantom) of the two sides of the line forming one side of the phantomand consequently do not introduce an impedance to the currentstransmitted over the phantom. The series condensers of the high passfilters, however, are included serially in the phantom circuits butthese condensers readily pass thehigh frequency carrier currents so thatthe effect of the filters HF and HR uponthe carrier currents transmittedover the phantom is relatively smalh p in order to provide the necessaryfre quency separation between the voice currents transmitted over thephantom and the carrier currents transmitted over the phantom,

a low pass filter LF is included in the voice phantom terminals VL and ahigh pass filter HF, is included in the carrier phantom terminal CLThese filters are similar to the high and low pass filter combinationsalready described and operate in the same manner. The necessity forthese filters arise from the fact that the conductors ol the voicephantom circuit are connected to the conductors of the carrier phantomcir cuit through the filters LR, and HF in series on the one hand. andthe filters LF, and HR in series on the other hand.

It will be obvious that the general principles herein disclosed may beembodied in many other organizations widely different from thoseillustrated without departing from the spirit and scope of the inventionas defined in the appendedclaims.

f-Jhat is claimed is:

1. In a transmission system, a pair of side circuits each adapted forthe transmission of voice frequency currents and also for thetransmission of carrier currents, a pair of terminal branches for eachside circuit, a low pass filter in one branch of each pair to permit thetransmission of voice currents over said branch while suppressing thetransmission of carrier frequency currents transmitted over theconductors of the side circuits in series, a high pass filter in theother branch of each pair adapted to transmit carrier currents fromcarrier terminal equipment to and from the side circuit while preventingvoice frequency currents from entering said branch, means to establishaphantom connection adjacent one end of said low pass filter associatedwith each side circuit to form a phantom circuit for the transmission ofvoice frequencies, means to establish a phantom connectionadjacentoneend of said high pass filter associated wlth each sidecircuit to form a phantom connection for the transmission of carrierfrequencies, a low pass filter in said first -mentioned phantomconnection to permit the voice frequency currents to be transmittedthereover while suppressing carrier frequency currents, and a high passfilter in said second mentioned phantom connection to permit carrierfrequency currents to be transmitted over said second mentioned phantomconnection while suppressing voice frequency currents therefrom. i

2. In a transmission system, a pair of trans mission lines adapted totransmit either ordinary voice frequency currents or carrier frequencycurrents, a pair of branches for each line, one branch extending to avoice frequency terminal and the other branch extending to carrierequipment. alov: pass filter in ,said first mentioned branches of: eachline and a high pass filter in said second mentioned branches or"eacnrline, means to connect a phantom conductor to the first mentionedbranches of each line, a low pass filter included in the phantomconductors thus formed so that voice frequencycurrents may betransn'iitted over said phantom, means to connect a phantom conductor tothe second mentioned branches of each line, and a high pass filterincluded in the phantom circuit formed by means of'sa-id secondmentioned branches whereby carrier currents may be transmitted over saidsecond mentioned phantom circuit to the exclusion of voice frequencycurrents.

'3. In a transmission system, a pair of transmission lines adapted totransmit either voice frequency currents or carrier frequency currents,a pair of branches for each line, one branch extending to a voicefrequency terminal and the other branch extending to carrier equipment,a-low pass filter in said first mentioned branch of each line and a highpass filter in said second mentioned branch of each line, said low passfilter comprising a plurality of sections each of which consists of aseries inductance and a shunt in'ipedance element, said high pass filtercomprising a plurality of sections each of which consists of a seriescapacity and shunt impedance element, a phantom coil interposed betweensaid low pass filter and said voice frequency terminals for each line, aphantom conductor connected to the midpoint of each phantom coil so thatthe two phantom conductors establish a Voice frequency phantom circuit,a low pass filter included in said phantom circuit, a phantom coilinterposed between said high pass filter and said carrier terminal foreach line, a phantom conductor connected to the mid point of each ofsaid last mentioned phantom coils so that the two phantom conduc torsestablish a carrier frequency phantom circuit and a high pass filter insaid carrier frequency phantom circuit;

In testimony whereof, I have signed my name to this specification this10th day of August,1925. I

HERMAN A. AFFEL.

